He wrote, "You want to keep in mind that the users (and also our algorithms) prefer unique and compelling content." But if you can't, then what?

Gary wrote that you must have elements that are unique.

If having 100% unique content is not possible, the webmaster should make sure to have elements in the pages that are unique and valuable for the users, give a good reason for them to visit the site.

There are plenty of sites that do not 100% unique content, including this one (clearly, since I quote threads) but adding value on top of that content by aggregating it, adding context and tools on top of it - that can be the "element"(s) that are "unique and valuable."